Magnetic device



H. F. PORTER MAGNETIC DEVICE May 5, 1931.

Filed Sept. 28, 1928 0 2 Sheets-Sheet 1 mo y. a 3% AW wwafl F W 13 m 8 wy 1931. H. F. PORTER 1,803,868

MAGNETIC DEVICE Filed Sept. 28, "192 2 Sheets-Sheet 2 fliiior-negsmoothing efi'ect.

Patented May 5, 1931 UNITED STATES HARRY I. PORTER, OF TRENTON, NEWJERSEY MAGNETIC DEVICE Application filed September 28, 1928. Serial No.309,086.

My invention relates to magnetic devices, and more particularly toreactor structure.

My invention resides in a reactor for substantially eliminatingpulsations or varia- 5 tions in amplitude of a direct current, wherein ac011 traversed by said current is substantially enclosed by structure ofmagnetic material.

My invention further resides in a reactor 10 of the above characterwherein the coil is disposed within an annular recess of a member ofmagnetic material which co-operates with another member of magneticmaterial to complete a magnetic circuit; furthermore the materialcomprising said magnetiaable structure prefera ly has a comparativelyhigh initial permeability and high electrical resistivity.

My invention further resides in a reactor of the above character whereinthe members of magnetizable material substantially enclosing said coilare spaced to form an air gap centrally of the coil; furthermore, atleast one of said members is a casting or forging.

My invention resides in structure of the character hereinafter describedand claimed.

The development of the alternating current receiving or transmitting setin radio apparatus and telephone amplifying equipment has directedparticular attention to the proper design of smoothing reactors foreliminating the fluctuations or ripples generally existing in therectified current. In a smoothing reactor, the core or magnetizableelement is polarized by a fairly heavy direct current and acomparatively small fluctuating field is produced by the aforesaidcurrent ripples, which of necessity must be eliminated by the smoothingreactors and associated apparatus in order that objectionable hum maynot appear in the tone reproductions.

Heretofore smoothing reactors used in combination with condensers in theusual manner have only partially eliminated the hum, due to the factthat a small stray or leakage field generally exists outside of thereactors, thereby preventing a perfect y invention comprehends apparatusfor substantially eliminatmg the ripples in the direct current, and inpreventing stray or leakage field of the reactors from existing outsideof their core members.

For a better understanding of my invention, reference is to be had tothe accompanying drawings in which:

Fig. 1 is a top plan view of a smoothing reactor constructed inaccordance with my lnventlon.

Fig. 2 is a sectional side view taken along the line 22 of Fig. 1.

Fig. 3 is a view taken along line 3-3 of Fig. 2 with the coil elementremoved.

Fig. 4 is a sectional view of a modified form of my invention.

Fig. 5 is a view artly in section of another modification o f myinvention.

Fig. 6 is a view partly in section of another modification.

Fig. 7 is a view in section of another modification.

Fig. 8 is a view in section of another modification.

Fig. 9 is a diagrammatic illustration of a system for rectifyingalternating current having included therein smoothing reactors andcondensers.

Referring to Figs. 1 and 2, a cast or forged member 1 being cup-sha d inform comprises an outer annular ange 2 and a centrally disposed hub orboss 3 which has a bore 4 extending centrally therethrough. Casting 1 isof magnetic material of the character hereinafter described and has aslot 5 extending diametrically across the entire top section, throughthe central boss 3, and partly through the outer flange 2. Slot 5 may becut in casting 1 by a. circular cutter, which would enable the slot toextend entirely through boss 3 without entirely separating the castingsin halves. It will be understood that in the above structure, and thathereinafter referred to, a plurality of slots may be used if desired andmay extend either parallel with each other or radially with respect tothe castin has holes 6 bored therethrougfi for permit- Member 1 tingconductors 7 to extend to the inner side of member 1.

The outer flange 2 together with the top portion of casting 1 andcentral boss 3, form an annular recess 8 in which a coil 9 is adapted tobe seated. Coil 9 may be of any suitable desi depending on theinductance required an portion fitseasily over boss 3. A second castingor equivalent, of magnetic material 10, is adapted to co-operate withmember 1 so as to substantially enclose coil 9 and to complete themagnetic circuit around the same. Member 10 may be of exactly the samedesign and construction as member 1, in that it also has a side flangeand central boss 12 forming an annular recess 13 for also enclosing aportion of coil 19.

Referring to Fig. 2 the diametrically extendin slot of member 10 isillustrated as extending vertically. Non-magnetic securing means, as abrass bolt 16 having threaded ends on which nuts 17 are mounted, extendthrough the central bores 4 of bosses 3 and 12 to clam members 1 and 10firmly together at the e ges of their outer flanges. Bosses 3 and 12,however, are ground down, or otherwise reduced in height, so that an airgap 14 is formed between adjacent portions thereof when members 1 and 10are clamped together about coil 9 to form a unitar structure. The widthof air gap 14 may o viousl vary in accordance with the particular esignrequirements of the smoothing reactor. The terminals of coil 9 areelectrically connected to conductors 7 which are led through casting 1in the manner previously described. I

Fig. 4 illustrates a modification of my invention in which a cup-shapedmember 18, of substantially the same. design as member 1, has aplate-like or equivalent member 19 of magnetic material cooperatingtherewith, instea of another cup-shaped member. Member 18, as shown, hasa slot extending vertically therethrough, and comprises an outer flange20 and a central inner boss 21 forming with the side portion of member18 an annular recess 22 within which is seated coil 9. Recess 22 issubstantially deeper than recess 8 shown in Fig. 2, so that coil 9 isentirely within the said recess. The plate 19 of magnetic material issnugly clamped to the edge of outer flange 20 in any suitable manner,and is spaced by an air gap 23 from boss 21. The air gap 23between-members 19 and 21- may be accurately formed b grinding ofi apredetermined amount 0 boss 21, or by forming a depression in member 19.

In the modification illustrated in Fig. 5, substantially the samestructure as shown in Fig. 4 is utilized with the exception that asecond coil may be used in connection is soshaped that its centraltherewith bymproviding a second coil enclosing mem r for co-operatingwith plate 19. One coil may be disposed within recess 22 of member 18,and the other coil within recess 25 of member 26. i The edges of flange24 abut against and are secured to plate 19. as Well as to member 18 byany suitable means, so that the magnetic element 19 serves as a commonpath for flux produced by both coils. The width of plate 19 may 0viously vary in accordance with flux density requirements, and the airgap 27 formed between boss 28 and member 19 may be the same as, ordiffer from air gap 23.

Figs. 7 and 8 each disclose modifications of the structure shown in Fig.5 whereby there will be a predetermined amount of mutual inductancebetween the two coils. It is sometimes advantageous, for reasonshereinafter e2? lained, that there be a certain degree 0 mutualinductance between the coils in rectifier circuits.

Referring to Fig. 7, which is identical in structure to Fig. 5, exceptfor the construction of plate 19, an aperture 61 is provided in saidlate for permitting a certain amount 0 flux of one coil to traverse themagnetic circuit of the opposite coil. The construction of the twomagnetic circuits being symmetrical, it will be apparent that there willbe mutual inductance between coils 62 and 63 to an equal degree. Thesize of aperture 61 may be varied to change the degree of mutualinductance, this change being proportional to the change in size of theaperture. When the aperture exceeds a certain sizeit will be apparentthat the two coils will act as a single choke, provided of course thatthey are connected in such way that their magnetic fields are not inopposition to each other.

Referring tothe construction shown in Fig. 8, plate 19 is shown having asingle aperture 64 of slightly larger dimensions than the cross-sectionof boss 65. In this modification, the construction of the magneticcircuits is not symmetrical with respect to their respective coils-"Boss 65 extends through aperture 64 for a short distance be ond plate19 and is spaced from 3 boss 66 y an air-gap 67 of predetermined width.The normal magnetic circuit of coil 62 will therefore have greaterreluctance than the normal magnetic circuit of coil 63, since it willcomprise air gap67 in addition to the air gap formed by the spacebetween boss 65 and plate 19. The normal magnetic circuits of coil 63includes but one air gap, which is simply the space between boss 65 andplate 19, and the amount of flux traversing the magnetic circuit of coil62 through air gap 67 will depend on the ratio of the dimensions of thetwo air gaps. In other words, if boss 65 was in fairly snug engagementwith plate 19 there would obvilOfi lflfl ously be a very small amount ofleakage flux through air ap 67 to the magnetic circu1t of 0011 62f n theother hand, flux produced by coil 62 would traverse air gap 67 5 andthen flow inparallel through both plate 19 and boss 65 through themagnetic circuit of coil 63. In such an event there would be a decideddifference between the inductive effects of coils 62 and 63 on eachother, coil 62 of course having far greater inductive effect upon coil63.

It w1ll be apparent therefore that by varying the size of aperture 64,and thereupon varying the dimensions of the air gap between plate 19 andboss 65, the ratio of mutual inductance, as well as the degree thereofbetween coils 62 and 63, may be controlled. To effect this adjustment,any suitable means for varyinFg the size of aperture 20 64 may beutilized. or example, plate 19 may be separated through its diameterinto halves and suitable adjusting means may be provided to move thehalves with respect to each other and therefore vary the size ofaperture 64.

In the modification illustrated in Fig. 6, there is shown structure forsubstantially completely shielding one coil from the field of another.Two cup-shaped members 80 and 31 of the character previously describedhave inter osed between them a member 32' of'magnetic material havingbosses 33 and 34 extending centrally thereof. Members 30 and 31 havebosses 35 and 36, which are 85 approximately only about one-half as highas the corresponding outer flanges 37 and 38. Bosses 35 and 33 aredesigned to form an air gap 39 ofpredetermined width, and bosses 34 and36 are also desi nod to form an air gap 40 of predetermine width whenthe edges of flanges 37 and 38 of members 30 and 31 are clamped orsecured to member 32. In the construction illustrated, air gaps 39 and40 are remotely positioned with respect to each other, and there issmall danger of stray or leakage flux penetrating to the opposite coil.Moreover, member 32 is of such thickness that the coils are magneticallyshielded from each other to a complete so extent.

Fig. 9 dia rammatically illustrates a system for utilizing rectifiedalternating current in connection with radio circuits. 'A

. source of alternating current 41, which maybe the usual 110 volt housesupply, is

connected to a transformer 42 having a primary 43. and individualsecondary coils 44and 45. A rectifying tube 46 has its filament 47heated directly through secondary e0 44. The opposite terminals ofsecondary 4') are connected individually to the anodes 48 and 49 of therectifying tube which cooperates with the filament or cathode 47 foreffecting double wave rectification of the .66 alternating current.Secondary 45 has a central tap 50, to which is connected conductor 51having in series therewith individual smoothing reactor coils 9..Reactors 9, in the present application thereof,

may sometimes be mutually inductive to a" reactor coils, the resultantdirect current potential being impressed across plate 56 arid filament53. For the sake of convenience filament 53 is shown as heated by a cell57,'although in alternating current sets the filaments are generallyheated directly by the alternating current.

By insertion of smoothing reactors of the character herein described inthe system shown in Fig. 9, the fluctuating direct current potentialbetween plate 56 and filament 53, which in the past has not been en-'tirey eliminated, may be corrected. These fluctuations in the D. C.potential are of course of audio frequency, and if noteliminated willproduce the objectionable hum which detracts greatly from the quality ofthetone reproduction.

Although in the present instance the cupshaped member of magneticmaterial has been particularly described as a casting, it will beunderstood that the said member may take other forms, such as a forgingor structure comprising built-up laminations, for example, if sodesired. There are, however, several important practical advantages inusing castings or forgings instead of a laminated structure, and forthat reason they are preferred.

Since the alternating component of the flux in the core of a smoothingreactor is very small as compared with the main direct current flux, thehysteresis and eddy current losses are rarely the limiting factor ofdesign. For this reason the use of laminated structure is not onlyunnecessary but more expensive and therefore solid sections, ascastings, are entirely practical. Furthermore from a viewpoint ofmanufacture and assembly the advantages of castings and forigings areapparent.

eferring to Fig. 2, for exmple. there is shown but a single securingelement for holding the two castings together and makingthe same acomplete unitary structure. The castings themselves moreover serve bothas container and mounting for the coil. and effect perfect magneticshielding of the unit.

Since a casting is obviously more compact 'than laminated structure fora given crosssectional magnetic area, it follows that considcrably lessspace is required for mounting the reactors, and due to the perfectmagnetic shielding previously referred to, close spacing of the reactorw1th respect toother parts of the circuit is therefore permitted.

The location of the air gap in a smoothing reactor is of particularimportance .since elimination of leakage flux is an essentialrequirement, and since the air gap when the parts are assembled shouldbe of predetermined width in the case of accurate reactor design. Bylocating the air gap in the cent r of the unit as illustrated in Fig, 2,l akage field is obviously eliminated since all the flux traversing airgap 14 must necessarily return by way of outer flanges 2 and 11 ofcastin s 3 and 10. From a standpoint of accurate design, it is clearthat by grinding boss 3 a predetermined distance below the plane of theedge of flange 2, and by grinding boss 12 in the samemanner an air gap14 of predetermined width is formed which will be constant as long ascastmgs 3 and 10 are firmly clamped together at their outer edges bybolts 16.

It will be seen therefore that the air gap is not only accuratelyformed, but is malntained constant at all times. -This is not entirelytrue of reactors which are so assembled that mechanical shock may varythe width of the air gap to a slight degree, and so materially vary thereluctance of the magnetic circuit.

The dimensions etc. of the air gap and coil are designed to meet therequirements of the particular circuit in which the smoothing reactor isto be used-in accordance with well known rules and laws.

The structure shown in Fig. 4 from a magnetic standpoint is'entirelysuitable for use as a smoothing reactor, in that there is perfectmagnetic shielding of the e011 and no leakage field due to air gap 23exists outside of the unit. Applicant has found that a soft ironsub-panel, such as 19, not less .than one-sixteenth of an inch thick, issufiicient for magnetic purposes, although a thicker plate from amechanical standpoint would be desirable so that the plate may havesuflicient strength and rigidity to resist shock which would tend towarp plate 1.) and so vary the width of air gap 23. I have found that 4%silicon steel is the best material obtainable at present for plate 19.

\Vheii two reactors of the type shown in Fig. 4 are clamped end to endby non-magnetic fastening means, with but .008" nonmagnetic spacin-between the end plates 19, no measurable coupling or interaction canthere? is no external magnetic field of either nit. r

In the structure shown in Fig. 5 panel 19 is entirely protected bycastings 18 and 26,

and I have found that by using a soft iron panel only one-sixteenth ofan inch thick, there is but slight mutual inductance between the coilsseated in recess 22 and 25 respectively.

The structure illustrated in Fig. 6 removes all possibility of anyinteraction between the coils due to the opposite air gaps, and coilslocated in recesses 37 a and 38a respectively are as perfectly shieldedfrom each other as if they were enclosed in individual units of the ty eshown in Fig. 2.

The material of w ich the castings are made may vary in accordance withthe different requirements for the reactor. I have found that 4% siliconsteel castings, with carbon'l/lOOth of 1% or under, is best from apractical standpoint when the total ampere turns of direct currentexceeds 100. In other words 4% silicon steel castings are preferred formost rectifier circuits since in such cases the number of ampere turnsgenerally exceeds 100, I However, where the number of ampere turns isless than 100, I have found that a special alloy of nickle, copper andiron, bearmg the trade name A- metal, is more economical and givesbetter results. The field of the latter ap lication is in audiofrequency impedances w ere impedance coupling is used.

The'preferred magnetic material for the castings or forgings has suchcharacteristics that the product of the initial permeability and theelectrical resistivity is a maximum. As this product approaches amaximum the inductance per turn of the coils will increase and thelimits of frequency at which the smoothing of these reactors iseffective will be lower. tively high frequency pulsations m'osteffectively, an alloy of lower electrical resistivity may be employed,or a short-circuited turn, as a copper annular ring may I beincorporated. within the cup-like container for the coil or coils.

For example, a choke designed to operate most efficiently at60 cycleswould not necessarily be equally as efiicient at 540 cycles. In thelatter case, a fairly heavy short-circuited copper turn or annular ringwill reduce the effective inductance of the choke for 60 cycles but willgive better smoothing characteristics at 540 cycles. Similarly an alloyof somewhat lower resistivity may be used to advantage at the higherfrequencies.

The use of A-metal is particularly advantageous where the alternatingflux density is reduced to very small values, the D. C. magnetizingforce being substantially constant, since A-I'netal prossesses acharacbe detected. This establishes the fact that teristic known as highinitial A. C. perme- If it is desired to smooth rela-- ability. It is awell known fact that for a given value of alternating flux density, thevalue of A. C. permeabihty decreases with increases of D. O. fluxdensity. This is a property common to all ferro-magnetic materials. TheA. C. permeability has no direct dependence on 'dB/dH, or themathematical slope of the D..C. magnetization curve. If the value of theA. C. flux density is reduced to very small values, the D. (J. fluxbeing constant, the A. C. permeability of iron and its alloys approachesa definite limiting value. This limiting value of A. C. permeability isusually called initial A. C. permeability.

B utilizing metal of comparatively high A. initial permeabilitycharacteristics, as A-metal, the reactor may obviously be more eflicientwithin the vrange of small changes in A. C. flux density.

I claim:

1. Reactor structure comprising a pair of cup-like members of manetizable material, a coil disposed in each 0 said members, and a plateof magnetizable material interposed between said members and forming apartition between said coils whereby mutual inductance of said coils iscontrolled.

2. Reactor structure comprising a pair of cup-like members ofmagnetizable material each having a centrally extending boss, a coilseated axially upon a boss in each of said-members, and a plate ofmagnetizable material interposed between said members, whereby amagnetic circuit for each coil is completed through its respective bossand cup-like container, said plate and an air gap between said plate andsaid boss.

3. Reactor structure comprising a pair of cup-like members ofmagnetizable material, each having a centrally extending boss formin anannular recess within said member, a 0011 seated within each of saidrecesses, and a plate of magnetizable material interposed between saidcoils forming a partition between said members, said plate having anopening therein for permitting mutual inductance of said coils to apredetermined degree.

4. A reactor comprising a member of magnetizable material havingcomparatively high permeability at low alternating flux densities, saidmember having an annular recess formed therein, and a longitudinallyslotted core member, a coil traversed by current whose direct currentcomponent is large relative to its audio frequency alternating currentcomponent disposed within said recess and about said slotted core, and asecond member ofsimilar magnetic characteristics completing with saidfirst member and slotted core a magnetic circuit traversed by fluxproduced by current in said coil.

5. A reactor comprising a solid member of magnetizable material havinghigh permeability at low alternating flux densities, said member havinga base portion, a flange normal thereto, and a core member slottedlongitudinally, a coil traversed by current whose direct currentcomponent is large rel ative to its audio frequency component disposedin 1 art .in an annular recess of said member ormed by said slotted coreand said flange, and second similarmember oppositely disposed withrespect to said first member with the slots of said cores in staggeredrelation-..

6. A reactor comprising a pair of solid magnetizable members each havinga base portion, a flange normal thereto, and a central core member, coilstructure enclosed by said members, and a non-magnetic member extendingaxially of said core members for holding said pair of members againsteach other.

7. A reactor comprising a solid magnetizable member having a baseportion, a flange normal thereto, and a core member forming with saidflange an annular recess, said member having a slot extending acrosssaid base portion and longitudinally of said core member, a coiltraversed by current whose direct current component is large compared toits audio frequency component disposed within said recess about saidcore, and a second magnetic member completing the magnetic circuitbetween said flange and said slotted core member.

8. A reactor comprising a pair of magnetizable members, each having anannular recess, coil structure disposed in said recesses, and a singlemember of non-magnetic material extending through said members axiallyof said coil for securing said members together, thereby enclosing saidcoil and forming a magnetic circuit for the flux thereof.

9. A reactor -comprising a pair of magnetizable members each having abase portion, a flange normal thereto, and a core member with a slotextending across the base portion, and longitudinally of said flange andcore member, and coil structure disposed within an annular chamberformed by the flanges and cores of said members.

10. A reactor comprising a cup-shaped member of magnetizable materialhaving high initial permeability at low alternating flux densities, acoil traversed by current whose direct current component is largecompared to its audio frequency alternating current component, and asecond member of magnetizable material engaging the periphery of saidfirst member completely to enclose said coil and spaced from the centralportion thereof to form an air gap internally of said coil, said memberhaving a continuous periphery and slotted to divide said member intoportions united only at said periphery.

11. A reactor comprising a coil traversed by current whose directcurrent component is large compared to its audio-frequency alternatingcurrent component, and cupsha ed members of magnetizable material havinghigh initial permeability at low al ternating flux densities enclosingsaid coil, each of said members having a continuous periphery engagingthe periphery of the other member and each slotted to divide it intoportions united only at the periphery, the slots of one member beingstaggered with respect to the slots of the other member.

12. A reactor comprising a coil traversed by current Whose directcurrent component is large compared to its audio-frequency alternatincurrent component, a cup-shaped member 0 solid cross-section and of amagnetic copper-nickel-iron alloy, and a second member of magnetizablematerial engaging the periphery of said first member to enclose saidcoil, said first member being slotted to divide it into portions unitedonly at said periphery.

HARRY F. PORTER.

